Device for surface mounting of components

ABSTRACT

The invention relates to an apparatus for surface mounting of components (201) on a support (106). The arrangement comprises a positioning device )102, 103, 104) for holding and moving the components to a mounting position relative to the support. A centering arrangement of two components (203, 204) movable towards and from each other and disposed to center the component from opposite sides concurrently with its movement to the mounting position is provided. The centering arrangement (203, 204) comprises two centering electrodes (300, 310) which are designed with recesses (301, 302, 305, 306) which are adapted to the form and the size of the different component types to be mounted. The centering electrodes moreover comprise electric contact members (307, 308, 706) which are intended to connect the component to an equipment for measuring its electrical properties.

THE OBJECTS OF THE INVENTION AND ITS MOST SIGNIFICANT CHARACTERISTICS

Pick and place machines for surface mounting of electronic componentsfetch the components from a magazine and place them on a substrate, e.g.in the form of a printed circuit board. The present invention relates toan apparatus which at low price provides a number of advantageousproperties in a pick and place machine, viz.:

mounting of component with extremely varying size, e.g. from 2×1.2 mm to34×34 mm without change of centering tool

centering of the component relative to the housing

centering of the component relative to the connecting leads

mechanical measurement of the component housing

mechanical measurement of the distances between the external connectingleads of the component

connection of the leads to a test equipment to measure its electricalproperties, and

centering and measurement of mechanical and electrical propertiesconcurrently with the movement of the component which means without timeloss under normal conditions.

THE BACKGROUND OF THE INVENTION AND PRESENT PROBLEMS

Mounting of surface mounted components involves a number of problemscompared to the old technique of mounting components, the leads of whichare mounted in holes. These problems are as follows:

(1) The components are placed on a surface. The mounting error willtherefore be continuously variable which leads to boundary problemsbetween acceptable and unacceptable mounting. The old art componentshave a binary mounting error which means that either all leads are intheir holes or they are not.

(2) There are different reasons for an increased interest to glue thecomponents before soldering. This puts increased demands on the mountingposition. Up till now the components have mostly been mounted onsoldering paste. During the soldering operation surface tensionphenomena will cause an automatic centering of the component. However,if the component is glued this centering effect will be eliminated.

(3) The components are small. The distance between the leads on acomponent old in the art is almost always 2.54 mm or more. For surfacemounted components it is 1.27 or 0.80 mm and will decrease in thefuture.

(4) Machines for mounting of components old in the art utilize guidingholes which are drilled in the same operation as those in which thecomponents should be mounted. The errors between the guide holes and thecomponent holes will therefore be relatively insignificant.

(5) The components are so small that they mostly cannot be provided withidentifying text. This increases the demand to measure the componentelectrically before mounting to ensure that the correct component willbe mounted.

Items 1-4 above will together present great difficulties when mountingcomponents with a lead distance of 1.27 mm and less by gluing. Theenterprise Elektronikcentralen i Denmark which is well known in theNordic countries has issued a study No. ECR-143 with the title "Leadlesscomponents" and in the fifth chapter, page 15, they have reached theconclusion that "from the present prerequisits the only solution now isto utilize manual mounting only and thereby introduce an opticalcorrection of certain tolerances".

The actual Swedish production of surface mounted components with thelead distances 1.27 and 0,80 mm is often handmade even in the simplercase when the components are not glued.

Existing machines for surface mounting reflect the statements madeabove. These machines can be divided into different types, namely:

specialized machines which can only mount components having a sizewithin very narrow limits, e.g. from 2×0.8 mm up til 3.2×2.0 mm. Thesemachines often have high capacity and a high price.

Module machines are built up by a number of mounting stations each ofwhich is specialized for a certain group of components of the same ofalmost the same size and design. Thus, a customer who uses manydifferent component types must have a number of modules and willtherefore have to pay a high price.

Machines without a centering operation fetch the components and movethem. Thus, all errors in the fetch point component position will remainafter the mounting operation.

The apparatus according to the invention makes it possible to arrangeboth effective centering and possibilities for connecting the componentto an electronic measuring equipment with a minimum of mechanicalcomponents.

DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the encloseddrawing Figures. Moreover, the application of the invention will beshown on a machine which operates with a fixed magazine, a circuit boardor substrate which is movable in the Y-axis direction and a carriagewhich is movable in the X-axis direction and on which the apparatusaccording to the invention is mounted.

FIG. 1 shows the main parts of the machine,

FIG. 2 shows the basic operating function of the centering device,

FIG. 3 shows a centering electrode for centering against the connectingleads and for connecting a three pole component to a measuring device,

FIG. 4 shows a centering operation for the external measures of acomponent with two rows of connecting leads,

FIG. 5 shows a centering operation against the connecting leads for acomponent with two rows of leads,

FIG. 6 shows a centering operation against the connecting leads for acomponent with four rows of leads,

FIG. 7 shows a centering operation and connection to a test equipment ofa three pole component,

FIG. 8 shows test connection for different kinds of multipolecomponents,

FIG. 9 shows the connecting electrode for the test of multipolecomponents, and

FIG. 10 shows a centering device which is adapted to the demands definedby the connecting electrodes for the test of multipole components.

The design of the machine appears on FIG. 1. It comprises a firstcarriage 101 which is movable in the Y-axis direction and on which thecircuit board 106 is mounted. Above this first carriage there is asecond carriage 102 which is movable in the X-axis direction. Thissecond carriage supports a lifting device 103 which is movable in theZ-axis direction and which is pivotable in the .0.-direction. The secondcarriage also supports a centering device 104 and a TV-camera 105.

DESCRIPTION OF THE FUNCTION

The elementary function of the centering device 104 appears from FIG. 2.The component 201 is lifted by the lifting device 103 by means of anunderpressure and can therefore be laterally displaced relative to thenozzle 202 without falling down. The centering operation is effected bymeans of shoulders 203 and 204 which can be laterally moved. They aremainly moved in synchronism which means, that if the shoulder 203 ismoved 1 mm to the right the shoulder 204 is simultaneously moved 1 mm tothe left. When the shoulders 203 and 204 are pressed together with thecomponent 201 between them the midpoint of the component 201 will belocated in the point where the shoulders 203 and 204 should have met ifthere had been nothing in between them.

By carrying out the centering operation once and then turning thecomponent 90° and performing the operation once again the component canbe centered both in the X-axis and the Y-axis. By establishing amovement of the shoulders which is sufficiently wide the centeringoperation of components with extremely varying size will be accomplishedwithout need for changing the centering tool. Under the assumption thatthe distance between the shoulders is measured with a suitabletransmitter it is possible to mechanically measure the external measuresof the component. By designing the shoulders as test electrodes theelectric properties of two pole components can also be measured duringthe centering operation. By designing the shoulders 203 and 204 in amore sophisticated way and by arranging a cooperation between themovement in the Z-axis and the .0.-axis of the lifting device furtheroptional properties can be achieved.

FIG. 3 shows one shoulder 300 of a pair of shoulders where three suchproperties have been realized. The two shoulders 300 and 310 areessentially symmetrical and are hereinafter called centering electrodes.The different parts of the shoulder 300 are described in connection withthe following Figures. The different sections (A-A, B-B and C-C) showwhich part of the centering electrode 300 the Figures refer to. Thecentering electrode 300 can in principle be made as a pattern board.

Thus, since the component has to be raised and lowered the centeringelectrode 300 can be given different functions at different levels. Atthe top of FIG. 3 two recesses 301 are shown which are used forcentering against the housing leads as described more in detail withreference to FIG. 6. The recess 306 has a similar function for housingswith other dimensions. The recesses 302 and 305 are used for a centeringoperation which is described more in detail with reference to FIG. 5.

On the level 303 two pole components to be used as resistances andcapacitors are centered and connected for electric tests. Thereby thegold plated surface 307 can be used as the first connecting electrodewhereas the other electrode is located on the opposed centeringelectrode 310. The level can also be used for centering biggercomponents before test connection.

In the lower level with the holes 304 three-pole components with threeand four leads as shown on FIG. 7 are centered and test connected.

The centering electrodes according to FIG. 3 provide a number of newpossibilities, viz.:

they accomplish centering of the component relative to the most criticaldimension of the connecting leads

they accomplish control measurement of the distance between the externalconnecting leads of the component

they accomplish connection of the three pole component leads to a testequipment for measuring its electric properties.

FIG. 4 shows how a component 404 (of the type SO-6), is centered at aconventional centering operation. The Figure shows a component with aconsiderable centering error between the plastic housing and the leads.Such error can arise if the plastic casting tool is erroneously centeredrelative to the group of leads or if so-called cast flash 401 has pouredout between the two halves of the cast tool. This last mentioned type oferror is common and creates problems in mounting machines. Even aperfect centering operation relative to the external measurement of thecomponent will in such cases give substantial error 402 between thecenter 403 of the mounting head and the center 405 of the componentleads. Mounting machines strive to place the mounting head straight overthe expected position of the component on the circuit board. A deviatinbetween the center 403 of the mounting head and the center 405 of thecomponent leads will therefore in average give rise to an equaldeviation in the position of the component.

FIG. 5 shows how the recess 305 in the centering electrode 300 could beused to center a component 501 of the type SO-6 directly against theconnecting leads 502. The Figure is taken in the plane which in FIG. 3has been marked with Section A-A. The component has already beencentered in one direction against the plane surface 303 in the waydescribed with reference to FIG. 2, and in the position shown in theFigure it is to be centered in the remaining direction. The Figure showsthe centering operation from below. Therefore, both of the centeringelectrodes 300 and 310 can be seen. The recess 305 in the centeringelectrode 300 will cause the electrode to hit the connecting leads 502during the centering operation.

FIG. 6 shows how the recess 301 in the centering electrode 300 can beused to center a component 601 against the connecting lead 602 in casethe component has connecting leads which project from all four sides.Depending on the size of the center deviations which are obtained whenthe component is fetched from the magazine the component will in suchcases probably have to be centered against its external measures of thesurface 303 before it is centered against the connecting leads by meansof the recess 301. The Figure shows the centering operation from above.Due to the recess 301 in the electrode 300 it will only make contactwith the connecting leads 602. The recess 306 in the centeringelectrodes 300 and 310 is not shown in the Figure since it is hiddenbehind the component body 601.

FIG. 7 shows centering and test connection of a three pole component bymeans of the hole 304 on the centering electrode 300. The Figure shows asectional view through the component and the position 304 on thecentering electrode.

The component 701 has four leads but only three poles since the leads703 and 705 are galvanically interconnected. The hole 309 in thecentering electrode 300 serves to ensure a safe contact against theleads 702 and 704 since the lead 703 cannot withstand any forces. On thesurfaces where the centering electrodes make contact against thecomponent leads 702, 704 and 705 there are provided test connections307, 308 and 706.

FIG. 8 shows a more complicated arrangement of connecting electrodes tomeasure components with more than three connections arranged in two rowsso-called dual in line. As an alternative the parts 801-806 can belocated in the same plane as the centering electrodes 300 and 310 andcould also be made of the same board material. FIG. 8 is seen from thesame view as FIG. 2. The parts 801, 803, 805 and 300 are built togethermechanically with mechanical parts 807 and they are moved in the sameway as the centering shoulder 203 shown in FIG. 2. The parts 802, 804,806 and 310 are moved in the same way as the centering shoulder 204. Theconnecting electrodes are built up in pairs 801-802, 803-804 and805-806.

FIG. 9 shows a test connection with one electrode in such a pair ofelectrodes which fits against a component 810. The other electrode inthis pair fits against the other side of the component but this is notshown on the Figure. The electrode has a number of resilient contacttongues 901 which make contact against the leads 902 of the component810. Since different component housings have different internaldistances between adjacent leads one furhter pair of electrodes isrequired for each lead distance. The same pair of electrodes can,however, be connected against components with different number of leadsprovided they have the same center distance between the leads.

When a device according to FIG. 5 is used one pair of leads will belocated just between the centering electrodes if the component has anodd number of connecting leads along each side. On the other hand aninterspace between the leads will be positioned between the centeringelectrodes if the component has an even number of connecting leads alongeach side. This involves a problem if a component thus centered shouldmake contact against a pair of electrodes 801-802. One solution could beto have different pairs of electrodes for components with an odd and aneven number of leads, respectively, along each side. A furtherpossibility would be to move the electrode pairs laterally.

FIG. 10 shows a much simpler solution with a pair of centeringelectrodes with two contact surfaces for the component leads. By meansof these surfaces the components can be centered so that the connectingleads in both cases can be placed in the same position relative to thecenter line of the lifting device. FIG. 10 shows a centering operationtaken from the same view as in FIG. 2. To illustrate the function theFigure shows a component with two by three leads 1005 in the lowestposition concurrently with another component with two by four leads 1006in the upper position. Practically only one component at the time can becentered. As appears from the Figure in both cases one pair of leadswill be positioned in line with the center line 1007 of the liftingdevice 103.

The operating sequence of the machine when it fetches, centers, controlmeasures and mounts a housing 810 of the type SO-8 will be describedbelow with reference to the drawing.

a component 810 (201) is in some way fetched and positioned under thenozzle 202,

if necessary, the component 810 (201) will be turned 90° so that it willbe positioned as shown in FIG. 8,

the component will be lifted to the level 303 at the centering electrode300,

the component will be centered in one direction by putting the shoulders203 and 204 together on which the centering electrodes 300 are mounted,

the size of the component will be measured in the actual direction inorder to reject mechanically defective components,

the shoulders 203 and 204 are moved apart and the lifting device 103 isturned 90° whereafter the lifting device 103 is raised so that thecomponent 810 will be on the same level as a corresponding recess, e.g.302, in the centering electrodes 300,

the shoulders 203 and 204 are again put together so that the component810 will be centered relative to the component legs in the remainingdirection,

measuring the component in the actual direction (to sort away anymechanically defective components),

moving the shoulders 203, 204 apart and turning the lifting device 10390°, lifting the lifting device 103 so that the component 810 is placedjust above the pair of electrodes fitting against the component, e g801-802,

again bringing the shoulders 203 and 204 together so that the resilientcontact tongues 901 will be positioned below the connncting legs of thecomponent 810,

lowering the lifting device 103 so that the component 810 is presseddown against the resilient tongues 901,

performing the measurement of the electrical properties of thecomponent,

raising the lifting device 103 so that the component 810 is releasedfrom the contact tongues 901 and moving the shoulders 203 and 204 apart,

turning the lifting device 103 so that the component 201 will obtaincorrect orientation,

waiting until the carriage 101 has reached the right place for mountingof the component 201,

waiting until the carriage 102 has reached the right place for mountingof the component 201,

lowering the lifting device 103 so that the component 201 is mounted onthe board or substrate 106.

A TV-camera 105 is used to determine the position of the board relativeto the coordinate system of the machine by moving the carriages 101 and102 until the TV-picture shows that the camera is positioned straightabove a reference point on the board. When the position for two suchreference points is determined a computer which controls the machine caneasily transfer the coordinates for the board or substrate to those forthe machine.

We claim:
 1. An apparatus for surface mounting of components on asupport, comprising a positioning device for holding and moving thecomponents to a mounting position in relation to the support, wherebycentering means are movable towards and away from each other and arearranged to center the component from opposite sides concurrently withits movement to the mounting position, characterized in that thecentering means comprises two centering electrodes which are providedwith recesses, the recesses having dimensions corresponding todimensions of the components to be mounted, and that the centeringelectrodes comprise electrical contact members to connect the componentsto an equipment for measurement of its electrical properties.
 2. Anapparatus according to claim 1, characterized in that the dimensions ofthe recesses of the centering electrodes correspond to dimensions of acomponent body, said body being introduced into the recess at thecentering operation, and lateral surfaces of the electrodes facing eachother being brought into contact with external connecting leads of thecomponent.
 3. An apparatus according to claim 1, characterized in thatthe component has a plurality of poles, and the centering electrodes areprovided with contact surfaces for making contact with the poles of thecomponent and with holes for those poles which are not connected to thecontact members.
 4. An apparatus according to claim 1, characterized inthat the centering means comprises connecting electrodes having a formof resilient contact elements against which connecting leads of thecomponent are brought into contact for measuring the electricalproperties of the component.
 5. An apparatus according to claim 4,characterized in that the connecting electrodes are disposed in opposedpairs with different numbers of contact tongues and/or different mutualdistances between the contact tongues for each pair of electrodes,whereby the electrode pairs are arranged on different levels above eachother.